Annealing method



for metals and metal.alloys.

Patented. 22, 1942 .No Drawing. Application February 9, 1940, Se-

rial No. 318,176. -In Germany My invention concerns anannealing method When annealing metals and metal alloys the surface of which would be altered under the influence-of oxy en of the atmosphere; it has been common practice for a longtime to perform the annealing in' a furnace, the atmosphere of which consists of a gas having a reducing effect upon the material to be treated or is ,at the least indifferent .to the material.

als, certain sensitive metals and alloys are attacked to such a degree by .the ox dizing constituents of the furnace atmosphere which can-- not be entirely avoided that it has not been possible up to now to anneal articles composed of these sensitive metals in a satisfactory mannerso that oxidation of their surfaces is avoided.- Alloys of this character are, particularly certaincopper alloys,'such as brass and, to a still higher.

- degree perhaps copper-silicon alloys.

v Fully satisfactory results are not attained by attempting to remove the oxides of the surface byetching methods as the etching of the annealed metal usually gives a dull surface. :f

The present invention makesjit possible to anneal articles composed of very sensitive metals and metal alloys without appreciable oxidation; or with a clean or bright surface, a so-called bright-annealing.

.According to this invention the annealing is performed not only in an atmosphere which has a reducing influence upon the material in ques tion or, at least, is inert with respect to said material, but, in addition, the articles to beannealed are coated or covered with reducing substances so as to'protect them against oxidatiom Through this covering or coating the contact (if the atmosphere of the furnace with the mate: rial to be annealed is prevented to a great extent. Any oxidizing gas particles of the furnace at mosphere which might nevertheless come into contact with the-article, can have no harmful effect because the reducing substance will prevent any oxidation or will reduce any oxidation which had already occurred. The protection of the articles to be protected from oxidation during annealing can be still further improved by tak; ing care to prevent relative movement between the goods-and the atmosphere of the furnace as Although this method gives sufll- 'cient protection against oxidation for many met- February 6,

1 Claim. (61. fix-13.2)

ablefor this purpose, preferably-metal powders comprising one or a plurality of the elements of the alloy to be annealed. Preferably metal powders should be applied which during the annealing process have apart from their reducing effect still the further. effect of entering into the surface of the material being annealed by diffusion. By suitable choice of the metals, a protective metallic covering can be obtained on the surface of the articles to be annealed. It is evident that the metals must be so chosen that the metal entering the surface by diffusion does not cause corrosion later on.

In a bright-annealing" treatment of articles consisting of a copper-silicon-alloy, a powder of v Y a copper-silicon alloy of high silicon content may beused as protective substance. A silicon content of 20% is suifi'cient to allow a pulverizing of the alloy. For the same purpose a powder of a copper-aluminum alloy may be applied. In this case the aluminum has not only a reducing effect, but it also enters the surface of the goods to be treated by diffusion and forms a cementation layer or'coating giving permanent protecthemselves may give suflicient protection against oxidation.

' If articles of elongated shape, such as bands.

far as possible. This may be achieved, for instance, by enclosing or packing the goods within a mass of the reducing material. However, the simple covering or coating of the reducing substance itself prevents any'considerable relative m vement between the articles and atmosphere.

a coating material for the goods to be annealed, amongst others,'pulverlzed carbon or coal are suitable on account of their high reducing qualities. Furthermore, metal powders are suitture.

rods, tubes or the like, are to be bright-annealed, it may be advisable to pass these elongated articles through layers of the reducing material loosely packed in the bottom of the furnace.

After the annealing has been performed, the protective substances, in dry condition, may be easily removed by should be found that for one reason or other the surface of the treated articles has a slight oxidation, which however will under no circumstances have a considerable thickness, this oxidation layer can be easily removed by etching without making the surface of the articles dull.

What I claim is:

A method of bright-annealing metal ina furnace having a substantially non-oxidizing atmosphere, the step of protecting"copper-silicon alloy against oxidation by impjirities of said atmosphere having .an oxidizing 'eflect on said metal by covering the metal with pulverized coppersillcon alloy, and heating to annealing tempera- OBKAR SUMMA.

Under certain circumstances such liquids as glycerine, petrol or the like in' rubbing or brushing. If it 

